Revealing mistake: There is a large painted hanging cloth backdrop of clouds in the mountain scenes near the end of the film. Vertical streaks can be seen in the backdrop that are the pleats in the fabric. These streaks really stand out in the restored versions of the film.
Other mistake: In the scene where Renfield enters Dracula's castle, it is past midnight and on the outside, it is dark. But there is a LOT of bright light streaming through the windows into the castle, throwing well-defined shadows. (00:09:10)
Twotall